Planning for the Impact of SC.24 on Spine Stereotactic Body Radiotherapy (SBRT) Utilization at a Tertiary Cancer Center

Abstract

<h3>Purpose/Objective(s)</h3> CCTG SC.24 was a recently reported randomized phase 2/3 trial that demonstrated superior complete response rates for pain following spine stereotactic body radiotherapy (SBRT; 24 Gy in 2 daily fractions) compared to conventional radiotherapy (CRT; 20 Gy in 5 fractions). These findings support a practice-changing paradigm shift whereby a subset of eligible patients with painful spine metastases may be offered upfront spine SBRT over CRT. At many institutions, this would mark an increase in spine SBRT cases. Therefore, we sought to assess the potential real-world impact of this study on spine SBRT utilization by estimating the proportion of patients treated with CRT who would have been eligible for spine SBRT per SC.24 inclusion criteria. <h3>Materials/Methods</h3> All patients who received palliative spine radiation at our institution between August to October 2020 were reviewed retrospectively. Data extracted included eligibility criteria of the SC.24 study, provider-reported pain response, and overall survival. Descriptive statistics and survival analyses were performed. <h3>Results</h3> Of the 73 patients reviewed, 24 (33%) patients met eligibility criteria for SC.24. The most common exclusion factors included irradiation of more than 3 consecutive spinal segments (n=32, 44%), ECOG greater than 2 (n=17, 23%), symptomatic spinal cord compression (n=13, 18%), and frank mechanical instability (n=12, 16%) as measured using the Spinal Instability in Neoplasia Score (SINS). SINS was indeterminable in 7 cases (10%) of epidural-only disease, which also renders a patient ineligible; otherwise, the median SINS was 9 (IQR: 7–10). Four (5%) patients had prior surgery and 8 (11%) patients had prior overlapping radiation to the area, also rendering them ineligible. Of eligible patients, the mean age was 68.92 years (SD 13.84), median SINS was 8 (IQR: 7–9) and median ECOG was 2 (IQR: 1–2). The most common primary cancer types among eligible patients were lung (n=10) and breast (n=4). The median dose delivered to eligible patients was 20 Gy in 5 fractions (IQR: 8–20 Gy). Fifteen (63%) eligible patients had additional radiation to a site other than the spine at the same time. The median survival of eligible patients was 10 months (95% CI: 4 months–not reached) with 58% surviving longer than 3 months. 75% of patients had pain response documented and of these, 54% had at least some response after CRT. <h3>Conclusion</h3> Around 1/3 of patients who received palliative CRT to the spine met eligibility criteria for SC.24. This possible expanded indication for spine SBRT can have a substantial impact on resource utilization. In addition to increased MR simulation utilization, there can also be higher demand on contouring, planning and quality assurance resources. These data may be useful in guiding resource and workforce planning at institutions looking to commence or expand a spine SBRT program.